1. Field of the Invention
The present invention relates to a heavy duty tire which can improve a durability of a bead portion.
2. Description of the Prior Art
In FIGS. 12A and 12B, there is shown a structure of a bead portion of a conventional heavy duty tire. The bead portion shown in FIG. 12A is structured such that a turnup portion “a” of a carcass ply is wound around a bead core b. The turnup portion a includes an end portion a1 extending along a radially outer surface bs of the bead core b. The end portion a1 is held between the bead core b and a bead apex c. Further, the bead portion shown in FIG. 12B has the turnup portion “a” of the carcass ply wound around the bead core b, however, a rubber g having a substantially constant thickness is arranged between the end portion a1 and the bead core b.
As in the above example, the bead portion having the turnup portion a wound around the bead core b is also called as a “bead wind structure”. In the bead wind structure, since an outer end of the turnup portion “a” is positioned near the radially outer surface of the bead core b, a stress applied to the end portion al of the turnup portion “a” at a time when a tire is deformed is small. Accordingly, it is possible to prevent damage such as a loose from the end portion al or the like. Further, since a length of the turnup portion a is short, the tire can be lightened. However, the bead wind structure has a defect that a loose of a carcass cord at an innermost end position Q in a tire axial direction of the bead core b tends to be generated, which has not been conventionally seen frequently.